1. Field of the Invention
The present invention relates to a liquid droplet ejecting apparatus and more particularly to the liquid droplet ejecting apparatus having a redispersion mode for redispersing cohered and sedimented solid particles of the ink to be ejected.
2. Description of the Related Art
Many types of liquid droplet ejecting apparatuses are presently used for personal, office, and industrial purposes. Two types of elements are used in these apparatuses to generate energy for ejecting liquids: elements which convert electric energy to thermal energy, such as heat generating elements, and elements which convert electric energy to mechanical energy, such as piezoelectric elements.
Liquids ejected from liquid droplet ejecting apparatuses are usually colored liquids such as black, cyan, yellow, and magenta ink. Inks can be divided into three types: homogeneous solution systems, disperse systems, and thermoplastic solids. Dyes provide color to solution-system inks, pigments provide color to disperse-system inks, and dyes, pigments, or both provide color to thermoplastic-solid inks.
Liquid droplet ejection apparatuses eject liquid droplets which impinge onto a printing medium, such as paper, forming an image thereon. Because images formed by disperse-system inks generally have a higher optical density than those formed from solution-system inks, disperse-system liquids are basically superior for producing high quality printed characters and diagrams.
However, there has been known a problem with liquid droplet ejecting apparatuses for ejecting disperse-system inks in that when not used for long periods of time, secondary cohesion of pigments and other solid materials of the disperse phase occurs from van der Waals force. Cohered solids of the disperse phase can clog nozzles in the recording head, causing liquid ejection misses. Also, the cohered solids can settle out of the dispersion medium, so that concentration of pigments in the ejected droplets is low at the start of printing, degrading quality of the printed characters and diagrams.
Presently, liquid droplet ejecting apparatuses for industry frequently use disperse-system inks. A complicated maintenance structure is often provided to industrial liquid droplet ejecting apparatuses for preventing or clearing clogging problems. Also users must perform periodic and often large scale maintenance.
Liquid droplet ejecting apparatuses for office and personal use, such as inkjet printers, also have similar problems when not used for long periods of time. Consequently maintaining stable quality of recorded images can be difficult. For example, because the nozzles in the printhead of inkjet printers are only a few micrometers in diameter, they are easily clogged by cohered particles of the disperse phase. Also, when recording is attempted while a large portion of the disperse phase is settled out of the disperse medium, the color of recorded images will be thin until the solids are redispersed. There has been a longstanding need for an apparatus that solves these problems to improve quality of liquid droplet ejecting apparatus which use disperse-system inks with pigments as the disperse phase.